Redundant backlight for electronic display

ABSTRACT

A first and second plurality of lighting elements are each configured to produce a desired overall luminance output for a backlight when illuminated at full power. If a measured luminance output is greater than a threshold, a controller supplies a non-zero power level less than full power to the first and second plurality of lighting elements. If the measured luminance output is less than the threshold, the controller increases the power supplied to only one of the first and second plurality of lighting elements, up to full power, to return the measured luminance output to at least said threshold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/257,620 filed Jan. 25, 2019, which is a continuation of U.S.application Ser. No. 13/159,183 filed Jun. 13, 2011, which claims thebenefit of U.S. Provisional Application No. 61/353,986, filed Jun. 11,2010, the disclosures of each of which are hereby incorporated byreference as if fully restated.

TECHNICAL FIELD

Disclosed embodiments relate generally to a backlight system for anelectronic display.

BACKGROUND OF THE ART

Liquid Crystal Displays (LCDs) contain several layers which work incombination to create a viewable image. A backlight is used to generatethe rays of light that pass through what is commonly referred to as theLCD stack, which typically contains several layers that perform eitherbasic or enhanced functions. The most fundamental layer within the LCDstack is the liquid crystal material, which may be actively configuredin response to an applied voltage in order to pass or block a certainamount of light which is originating from the backlight. The layer ofliquid crystal material is divided into many small regions which aretypically referred to as pixels. For full-color displays these pixelsare further divided into independently-controllable regions of red,green and blue subpixels, where the red subpixel has a red color filter,blue subpixel has a blue color filter, and green subpixel has a greencolor filter.

The light which is passing through each subpixel typically originates as“white” (or broadband) light from the backlight, although in generalthis light is far from being uniform across the visible spectrum. Thesubpixel color filters allow each subpixel to transmit a certain amountof each color (red, green or blue). When viewed from a distance, thethree subpixels appear as one composite pixel and by electricallycontrolling the amount of light which passes through each subpixel, thecomposite pixel can produce a very wide range of different colors due tothe effective mixing of light from the red, green, and blue subpixels.

Currently, the common illumination source for LCD backlight assembliesor Back Light Unit (BLU) is fluorescent tubes, but the industry ismoving toward light emitting diodes (LEDs). Environmental concerns,small space requirements, lower energy consumption, and long lifetimeare some of the reasons that the LCD industry is beginning thewidespread usage of LEDs for backlights.

LCDs are becoming popular for not only home entertainment purposes, butare now being used as informational/advertising displays in both indoorand outdoor locations. When used for information/advertising purposes,the displays may remain ‘on’ for extended periods of time and thus wouldsee much more use than a traditional home theatre use. Further, whendisplays are used in areas where the ambient light level is fairly high(especially outdoors or in aircraft cockpits) the displays must be verybright in order to maintain adequate picture brightness. When used forextended periods of time and/or outdoors, durability of the componentsespecially the illumination sources such as LEDs can become an issue.

As is readily apparent, an LCD will not function satisfactorily withoutan appropriate backlight system. The backlight is essential for properfunctioning as the image or data displayed on the liquid crystal layermay only be viewed while the backlight is providing proper illuminationto the liquid crystal stack. If the backlight system should failcompletely or operate at a less than optimal level, then the LCD willnot perform satisfactorily. While this may be a simple inconveniencewhen LCDs are used for entertainment purposes, when used for informationor data displays this can be very costly. For example, LCDs are nowbeing used in cockpits of aircraft as well as the instrument panels ordisplay in ground vehicles and marine equipment. In these applications,when there is a failure of the backlight, the LCD may no longer displaythe important information for the vehicle/aircraft and controls maycease to operate. These situations can be undesirable not only to thepassengers of the vehicle/aircraft, but also other soldiers who arecounting on this part of the mission.

LEDs, however, have a limited life span, and eventually their luminancewill degrade until little or no luminance is generated. Some LEDs mayquickly fail simply due to a manufacturing defect or may fail due toshock/forces applied to the aircraft or ground vehicle. Currently whenthis occurs in an LED backlight, the entire backlight assembly must bemanually replaced (i.e., the element which every LED is mounted to isreplaced with a new element containing all new LEDs). This is expensive,and is often time consuming. Alternatively, the LED backlight assemblycould be removed from the display housing, and the degraded or faultyLEDs could be manually replaced. This is typically even more costly, andinvolves extensive manual labor. In currently known units, this alsorequires virtual complete disassembly of the LCD to gain access to thebacklight. This complete disassembly is not only labor intensive, butmust be performed in a clean room environment and involves the handlingof expensive, delicate, and fragile components that can be easilydamaged or destroyed, even with the use of expensive specialized tools,equipment, fixtures, and facilities.

Thus, there exists a need for a more durable and dependable backlightfor a LCD so that failures can be accounted for and vehicles/aircraftcan complete a mission and/or return safely to base.

SUMMARY

Exemplary embodiments provide a light source for a display device havingprominent color reproducibility. Exemplary embodiments also provide alight source for a display device enabling thin and compact displayproduction continuously over extended use periods. In order to ensurecolor reproducibility and performance, the backlight of an electronicdisplay should preferably perform satisfactorily at all times.

Exemplary embodiments provide a backlight system for an electronicdisplay device, preferably an LCD device. The backlight system includesa first backlight apparatus and at least one additional backlightapparatus. The first backlight apparatus may be capable of providingsufficient light to operate the display. The second backlight apparatusmay be operated in the event that a portion of the first backlightapparatus falls below predetermined operational standards.

In at least one embodiment, there may be a backlight apparatus includinga first array of LEDs mounted on a printed circuit board (PCB).Additionally, there may be a second (redundant) set of LEDs mountedadjacent to the first array of LEDs. The redundant set of LEDs may bemounted on the same PCB as the first array of LEDs. Alternatively ifusing an edge-lit design, the first set of LEDs may be placed along afirst edge of the backlight while a second set of LEDs may be placedalong another edge of the backlight. A first control module may beassociated with the first array of LEDs while the redundant LEDs may becontrolled by a second control module. The two control modules may be ina master/slave arrangement where the first control module is the masterwhile the second control module is the slave.

The system may include a device for monitoring the luminance produced bythe first and/or second array of LEDs. The monitoring device may includepredetermined operational standards for the display. When the monitoringdevice detects that the display has fallen below the predeterminedstandard for luminance, the monitoring system may send a signal to oneor both control modules. If the first array of LEDs were the only sourceof illumination, the control modules can then switch to the second arrayof LEDs as there may have been a failure in the first array. The secondor redundant set of LEDs can be utilized seamlessly, thus ensuringcontinuous operation of the LCD without the need for costly and timeconsuming repairs of the backlight system.

Alternatively, the first and second array of LEDs may be poweredconcurrently. Operating the LCD in this manner allows the two LED arraysto operate at ½ the wattage while supplying the same amount ofillumination. This is noteworthy as LED efficiency (sometimes measuredas lumens per watt) is inversely related to temperature and by poweringeach LED at a lower wattage less heat is generated and the LEDs functionat higher efficiency. If one array were to fail, the other array couldadequately illuminate the LCD.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a front view of an embodiment for direct LED backlightingan LCD.

FIGS. 2A and 2B show front views for alternative embodiments of edge LEDbacklighting an LCD.

FIG. 3A shows a front view for an embodiment using edge LED backlightingan LCD where the both opposing sides of the LCD are illuminated.

FIG. 3B shows a front view for an embodiment using a combination of edgeLED backlighting and direct LED backlighting.

FIG. 4 shows an electrical schematic for an exemplary embodiment.

FIG. 5 shows exemplary logic for use with the devices of FIGS. 1-4.

DETAILED DESCRIPTION

FIG. 1 provides one embodiment showing a direct backlight assembly 100.A first plurality of LEDs 105 are mounted on a mounting substrate 150.The mounting substrate 150 could be any rigid or semi-rigid plate. Anexemplary embodiment would use a printed circuit board (PCB) as themounting substrate 150. A second (redundant) set of LEDs 120 are mountedadjacent to the first LEDs 105. The direct backlight assembly 100preferably generates white light. As shown in this embodiment, whiteLEDs are used to create the white light. Therefore, in this embodiment,for every LED in the first set 105, there is a corresponding LED for thesecond set 120 placed adjacent thereto.

Of course, there are many methods for generating white light and anymethod could be used with the embodiments herein. Some embodiments mayuse several colored LEDs in combination to create the color white.Sometimes this is done with red, green, and blue LEDs used incombination. Other times this may be done with a pair of LEDs whichcontain a red-green and a red-blue LED that combine to create white.

In one embodiment, the first plurality of LEDs 105 remain on duringnormal operation while the second plurality of LEDs 120 are off. If thesystem detects a failure in the first plurality of LEDs 105, the secondplurality of LEDs 120 may be turned on while the first plurality of LEDs105 are now turned off. The changeover from the first to second set ofLEDs can happen very quickly, so that there is no (or very minimal)interruption of the LCD operation when there is a failure in the firstplurality of LEDs 105. This design has been found to provide manybenefits. Notably, during operation of an aircraft or ground vehicle, afailure in the first plurality of LEDs 105 will not impact operation ofthe aircraft or vehicle where before this could cause catastrophicevents including the loss of control of the aircraft or vehicle.Further, the lifetime of the backlight device is effectively doubledwithout having to manually repair or replace the backlight.

As also illustrated in FIG. 5, in another embodiment, both sets of LEDsmay be operated simultaneously. This may be referred to as a first modeand is shown in step 610. In this embodiment, each set of LEDs may beoperated at only 50% capacity. This may be very desirable for LEDoperation as it can greatly increase the efficiency of the LED backlightand thus reduce the overall energy consumption of the device. Further,because the overall number of LEDs is effectively doubled, the lightdensity has increased and a more uniform level of light may be produced.In the event that one of the sets of LEDs may fail, the unit can beoperated sufficiently by only the remaining set of LEDs. In exemplaryembodiments, the failure of one of the sets of LEDs may be detected bymeasuring the luminescence as shown in step 620 and determining that themeasured luminescence falls below a desired output as shown in step 630.This changeover can also happen very quickly so that there would be no(or very minimal) interruption of the LCD operation. This may bereferred to as a second mode as shown in step 640. Stated another way,the system may automatically switch between a first mode and a secondmode. One set of the LEDs may be powerful enough to operate the LCDdevice at the desired brightness, color saturation, contrast, and anyother optical parameters set for the LCD device operation. In otherembodiments, one set of LEDs may be enough for the device to be viewableby the pilot or vehicle operator but may not be enough to operate at thedesired levels for an extended period of time. In this type ofembodiment, the remaining LEDs would allow the pilot or vehicle operatorto complete the mission and/or return to base but the LCD device mayneed manually serviced before the next mission.

As an extension of this embodiment, three or four sets of LEDs could beused to construct the backlight. Here, during normal operation each setof LEDs could be driven at only ⅓ or ¼ of the normal capacity, resultingin high efficiency and light uniformity. Upon failure of any one set ofLEDs, the remaining sets may be increased to provide the desired lightlevels. Again, this changeover can happen very quickly so that therewould be no (or very minimal) interruption of the LCD operation.

FIG. 2A shows an alternative embodiment using an edge-lit LED backlight200. As known in the art, edge-lit LED backlights place the LEDs alongone of the edges of the backlight so that they can provide illuminationinto the backlight cavity. This illumination is typically directed outof the backlight cavity and through the LCD stack as well as scatteredand/or diffused to provide a uniform light distribution. The scatteringand directing of the light can be accomplished in a number of differentways (light guides, diffusing sheets, etc.) and the details of this willnot be discussed in detail as it is well known in the art. For theedge-lit embodiment 200, the first plurality of LEDs 205 are placedalong a first edge while the second plurality of LEDs 220 are placedalong the opposing edge of the backlight. This design is beneficial inan embodiment where both sets of LEDs are operated simultaneously asthey could combine evenly to create a uniform distribution of light.Again, if the first set of LEDs 205 were to fail, the second set of LEDs220 could provide enough illumination so that the LCD device couldremain operational. The LCD device could be adequately powered to thedesired operation parameters with the remaining set of LEDs or maysimply be powered enough for the image on the LCD to be viewable so thatthe aircraft or vehicle could complete the mission and/or return tobase.

FIG. 2B provides another embodiment using an edge-lit LED backlight 300.Here, the first set of LEDs 305 is provided along the vertical edgewhile the second set of LEDs 320 is provided along the horizontal edge.Of course, there could be additional sets of LEDs provided along thebottom horizontal edge and the left vertical edge. In this type ofarrangement, the additional LEDs could correspond with the first orsecond LEDs 305 and 320 or may be third and fourth sets of LEDs whichare driven independently of the first and second sets of LEDs 305 and320.

FIG. 3A shows a front view for an embodiment 400 using edge LEDbacklighting for an LCD where the both opposing sides of the LCD areilluminated. Here, a first set of LEDs is comprised of two arrays ofLEDs 431 and 430 which are placed on opposing sides of the LCD.Additionally, a second set of LEDs is comprised of two arrays of LEDs420 and 421 which are placed on opposing sides of the LCD.

FIG. 3B shows a front view for an embodiment 450 using a combination ofedge LED backlighting and direct LED backlighting. Here, a first set ofLEDs may be provided in edge-lit fashion such that LEDs 461 are along afirst edge with LEDs 460 along an opposing edge. Additionally, a secondset of LEDs 480 is provided in a direct lit fashion.

FIG. 4 provides an electrical schematic for an exemplary embodiment. Afirst controller 515 is in electrical communication with a first currentsource 510 which drives the first set of LEDs 505. A second controller530 is in electrical communication with a second current source 525which drives the second set of LEDs 520. The electrical connection 575provides communication between the first controller 515 and secondcontroller 530. The first and second controllers 515 and 530 may be anytype of microprocessor, application-specific integrated circuit, complexprogrammable logic device, field-programmable gate array, or any otherform of electrical control. In some embodiments, the first and secondcontrollers 515 and 530 may be in a master/slave arrangement where thefirst controller 515 is the master and the second controller 530 is theslave. In this arrangement, the first controller 515 may provideadequate backlight luminance using just the first set of LEDs 505. Inthe event that the master controller (first controller 515) detects afailure in the first set of LEDs 505, it may direct the slave controller(second controller 530) to begin driving the backlight with the secondset of LEDs 520. A failure could be detected by measuring the currentdraw of the LEDs and when the measured amount falls outside of anacceptable threshold then a failure may have occurred. A failure couldalso be detected by measuring the luminance of the LEDs and indicating afailure when the luminance levels fall below an acceptable amount.

Having shown and described preferred embodiments of the invention, thoseskilled in the art will realize that many variations and modificationsmay be made to affect the described embodiments and still be within thescope of the claimed invention. Additionally, many of the elementsindicated above may be altered or replaced by different elements whichwill provide the same result and fall within the spirit of the exemplaryembodiments. It is the intention, therefore, to limit the invention onlyas indicated by the scope of the claims.

What is claimed is:
 1. A system for driving a backlight for an electronic display, said system comprising: a first plurality of lighting elements positioned to illuminate the electronic display, wherein the first plurality of lighting elements, when illuminated at full power, are configured to produce a desired overall luminance output for the backlight; a second plurality of lighting elements positioned to illuminate the electronic display, wherein the second plurality of lighting elements, when illuminated at full power, are configured to produce the desired overall luminance output for the backlight; and one or more controllers electrically connected to the first and second plurality of lighting elements, said one or more controllers each comprising software instructions, which when executed, configure the one or more controllers to: measure a luminance output of the backlight; if the measured luminance output is greater than a threshold, supply power at a first non-zero level less than full power to each of the first plurality of lighting elements and supply power a second non-zero level less than full power to each of the second plurality of lighting elements; and if the measured luminance output is less than the threshold, increase the power supplied to only one of the first or second plurality of lighting elements, up to full power, to return the measured luminance output to at least said threshold.
 2. The system of claim 1 wherein: each of the one or more controllers comprise additional software instructions, which when executed, configure the one or more controllers to supply substantially no power to the second plurality of lighting elements when the measured luminance output is less than the threshold.
 3. The system of claim 1 wherein: the first and second non-zero levels are substantially equal.
 4. The system of claim 3 wherein: the first and second non-zero levels are substantially half power.
 5. The system of claim 1 wherein: the first plurality of lighting elements comprise light emitting diodes (LEDs); the second plurality of lighting elements comprise LEDs; and the electronic display is a liquid crystal type display.
 6. The system of claim 1 wherein: said first and second plurality of lighting elements are arranged to provide direct backlighting to the electronic display.
 7. The system of claim 1 wherein: said first and second plurality of lighting elements are arranged to provide edge lighting to the electronic display.
 8. The system of claim 1 wherein: the first plurality of lighting elements are positioned in a direct-lit arrangement; and the second plurality of lighting elements are positioned in an edge-lit arrangement.
 9. The system of claim 1 wherein: the measured luminance output comprises data representing the current drawn by at least one of the first and second plurality of lighting elements.
 10. The system of claim 1 wherein: the measured luminance output comprises data representing the illuminance level provided by at least one of the first and second plurality of lighting elements.
 11. The system of claim 1 wherein: said one or more controllers comprise a first controller in electronic communication with the first plurality of lighting elements and a second controller in electronic communication with the second plurality of lighting elements.
 12. The system of claim 11 wherein: the first and second controllers are in a master/slave arrangement.
 13. A system for driving a backlight for an electronic display, said system comprising: a first plurality of lighting elements positioned to illuminate the electronic display and configured to produce the desired overall luminance output for the backlight when supplied with full power; a second plurality of lighting elements positioned to illuminate the electronic display and configured to produce the desired overall luminance output for the backlight when supplied with full power; and one or more controllers electrically connected to the first and second plurality of lighting elements and comprising software instructions, which when executed, configure said one or more controllers to: measure a luminance output of the backlight; supply a non-zero power level less than full power to each of the first and second plurality of lighting elements; if a failure is detected in one of the first or second plurality of lighting elements, increase the power level supplied to the remaining operable plurality of lighting elements up to as high as full power to return the measured luminance output a threshold.
 14. The system of claim 13 wherein: said one or more controllers are configured to cease applying power to the failed plurality of lighting elements.
 15. The system of claim 13 wherein: said one or more controllers are configured to detect the failure if the measured luminance output drops below the threshold.
 16. The system of claim 13 wherein: the non-zero power level less than full power is substantially half power.
 17. The system of claim 13 further comprising: a current source in electrical connection with the first and second plurality of lighting elements by way of the one or more controllers, wherein said one or more controllers are configured to detect the failure if the current draw from the current source drops to substantially zero.
 18. The system of claim 13 wherein: the first and second plurality of lighting elements are arranged to provide edge lighting.
 19. The system of claim 13 wherein: the first and second plurality of lighting elements are in a direct-lit arrangement; said first and second plurality of lighting elements are each comprised of light emitting diodes; and the electronic display is a liquid crystal display.
 20. A system for driving a backlight for an electronic display, said system comprising: a LCD stack; a backlight placed behind the LCD stack and comprising: a first plurality of LEDs; and a second plurality of LEDs; wherein the first and second plurality of LEDs are each capable of producing a desired overall luminance output for the backlight when full power is applied to the respective plurality of LEDs; at least one controller electrically connected to the backlight, wherein the controller is configured to: supply substantially half power to each of the first and second plurality of LEDs until the measured luminance output drops below a threshold; and increase the power level supplied to only one of said first or second plurality of LEDs, up to as high as full power, to return the measured luminance output for the backlight to at least the threshold, and supply no power to the remaining plurality of LEDs. 